Can't send email in Exch 2007 on SBS2008

I set up SBS2008. All is working correctly (Incoming internet email, Inter office email, RWW, OWA ...)
except I can't send external/internet emails.
I googled and tried various suggestions, but still it does not work.
In Exch Queue Viewer: 451 4.4.0 Primary target IP address responded "421 4.2.1
Unable to connect. "Attempted failover to alternated host, but that did not succeed.
Either there are no alternate hosts, or delivery failed to all alternate hosts".

Environment: Dynamic IP by Time Warner who confirmed they do not block outgoing emails.
Domain Name: mssonline.com
MX Record: Setup correctly according to mxtoolbox.com. But this IP address is trapped by
SORBS-DUHL & Spamhaus-ZEN due to the fact that it is DYNAMIC.
Smart Host: I am using it. I like to use my EXCH to host internet email
Ports on my Linksys Router: 25, 443 ,987, 4125
SEND CONNECTOR Configuration:
- FQDN : mail.mssonline.com (it showed remote.mssonline.com originally)
- Address Space: smtp * 1
- Network : Use domain name system ... automatically
- Souce Server : MSS01 which is the name of SBS Server
Edge Subscriptions: None created
Transport Rules: None created

Thank you for the suggestions. I tried them, but I still can't send email out. Here is what tried.
1. Port Check: OK on all the ports that I opened.
2. Connectivity Test: Checked for SMTP: SORBS Block List Status code: 10 SpamHaus Policy Block List (PBL)" Status code: 10 - This is expected due to nature of dynamic IP account that I have
3. smart host with your ISP in the send connector? – Not using it.
4. Does the server manager show the SMTP role installed? No When I tried to add additional Roles, SMTP role was not an option.
5. Is the server's IP the only entry in the DNS on the NIC tcp/ip? YES
The suggested link suggested 127.0.0.1 in DNS of TCP/IP. I tried, but the result is the same.
6. Is IPv6 enabled? Yes
7. Have you configured forwarders on DNS Server? Yes. I have two DNS server addresses by Time Warner
8. External DNS Lookups,select Use these DNS Servers, enter your ISP DNS server - YES I did.
9. In Organization Configuration > Hub Transport > Send Connectors, right click Windows SBS Internet Send and select properties, under Network tab put a check the box that says "Use the External DNS Lookup settings on the Transport Server" - YES I checked it.

All of these suggestions still result in the same error in the EXCH queue viewer - "451 4.4.0 Primary target IP address responded "421 4.2.1
Unable to connect. "Attempted failover to alternated host, but that did not succeed.
Either there are no alternate hosts, or delivery failed to all alternate hosts"

I ended up talking to Microsoft Exchange Server Engineer to get this resolved because I could not resolve the issue with information given on this board.

The internet email started going out as soon as I used my ISP's (Time Warner/Road Runner) SMTP server in Exc Mgmt Console/Organization Configuration/Hub Transport/Send Connectors/Default Windows SBS Internet Send Properties/Network Tab/Check for "Route Mail through the following smart hosts".
and Entered smtp-server.columbus.rr.com. Basically if you use Time Waner High Speed Internet Service, you must use their SMTP server name in your OUTLOOK or OE or Exchange Server because port 25 is being used by T.W. RR.

Exchange organizations may use the Journaling Agent of the Transport Service to archive messages going through Exchange. However, if the Transport Service is integrated with some email content management application (such as an antispam), the admini…